Modern advanced technology extensively requires various sorts of linear motion guide units, especially, linear motion guide units of the type using rolling elements of cylindrical roller, which are also required to live up to various operating performances including high precision, high stiffness, high sliding velocity, high acceleration/deceleration, less noise, and so on. To cope with this, there have been conventionally provided linear motion guide units in which separators are interposed between any two adjoining rolling elements.
In Japanese Utility Model Laid-Open No. S63-69816, there is disclosed a linear guide unit that is comprised of a retainer of synthetic resin to accommodate therein a cylindrical roller for rotation in a way exposing any part thereof, a slider made therein with a circulating circuit to allow the cylindrical roller rolling through there, and a guide rail to support the slider thereon for linear movement through the cylindrical roller. With the linear guide unit stated earlier, the retainer is shaped like doughnut and made circular in transverse section around parts where any adjoining retainers in the circulating circuit might come into direct contact with one another. The leading and trailing rollers are received in their respective retainers in such a relation that their inter-axial distance is kept constant throughout the circulating circuit. Moreover, the retainer is made on the outside thereof with shoulders while the guide rail has recesses to fit over the shoulders of the retainer to guide steady the roller along the circulating circuit. The shoulders are made midway between radially opposite rolling surfaces of the cylindrical roller, which are raised above the retainer to expose themselves outside the retainer.
In production of the retainer having the shoulders on the outside thereof, the cylindrical roller is first placed inside a mold of a casting machine preparatory to injection molding of synthetic resin. The retainer in the linear guide unit constructed as stated earlier is envisaged keeping the adjacent rollers against direct collision with one another, making collision noise less while protecting the cylindrical roller against wearing away, thereby making sure of steady operation of the linear guide unit. Nevertheless, the retainer constructed as stated just earlier, as being made to cover the overall axial length of the roller, unfortunately needs the circulating circuit larger in diametral dimension of a passage caliber, making the linear guide unit itself bulky. This means that the prior retainer as recited earlier is not suited to shrink the linear guide unit in construction. The retainer of the type in which the roller fits with molding, moreover, is not ready for modern operating needs for high traveling speed, high acceleration/deceleration, and so on because a clearance left between the retainer and the roller is so tiny to trend to cause lubrication failure. With the prior linear guide unit constructed as recited earlier, furthermore, as the leading and trailing retainers in the circuit come into direct contact with one another around their outside convexes, the pitch or distance between the adjacent rollers gets inevitably greater while the circular length of the exposed area on the roller also gets shorter. This results in making the linear guide unit less in mechanical strength.
Another Japanese Utility Model Laid-Open No. S63-123824 discloses a roller retainer of synthetic resin constructed to embrace a rolling element therein in a way the rolling element is exposed in part outside at a circular rolling surface thereof, where the rolling element comes into rolling-contact a guide rail while a slider moves along the guide rail. More than one roller retainer is disposed in succession in a circulating circuit of the slider. The retainer is provided at the leading edge thereof with a raised portion nearly halfway in vertical direction, and also cut away partially at the trailing edge thereof to make a window in complementary relation to the raised portion of the following retainer to expose outside only the trailing surface of the rolling element through there. Thus, the raised portion of the retainer is brought into abutment against the exposed trailing surface of the preceding rolling element through the window of the retainer ahead of the raised portion of the retainer. Moreover, the retainer is made on the widthwise opposed sides thereof with sidewise raised portions to fit into their associated guide grooves cut deep in the circulating circuit. In production of the retainer constructed as stated earlier, the cylindrical roller is first placed inside a mold cavity of a casting machine preparatory to injection molding of synthetic resin. The retainer is envisaged keeping the adjacent rollers against direct collision with one another, making collision noise less while protecting the cylindrical roller against wearing away, thereby making sure of steady running movement of the rollers. Moreover, the rollers in the circulating circuit may be easily varies in number.
Nevertheless, the retainer constructed as stated just earlier, as being made to cover the overall axial length of the roller, needs the circulating circuit larger in diametral dimension of a passage caliber, making the linear guide unit itself greater in construction. This means that the prior retainer as recited earlier also is not suited to shrink the linear guide unit in construction. The retainer made at the leading edge thereof with the raised portion while cut away partially is intricate in construction, which would need too sophisticated mold cavity in the injection molding process to prepare for the roller very small in diameter. The retainer of the type in which the roller fits with molding, moreover, is not ready for modern operating needs for high traveling speed, high acceleration/deceleration, and so on because a clearance left between the retainer and the roller is so tiny to trend to cause the issue of lubrication failure.
Another sort of linear motion guide means is disclosed in the Japanese Patent Laid-Open No. S50-130952, in which a part having a flat race surface is supported for reciprocating movement in longitudinal direction on a guide member. With the prior linear motion guide unit recited here, the rolling elements are successive in series inside the circulating circuit in a way each couple of any leading and trailing rolling elements is held within a common retainer high in mechanical stiffness. The retainer is made of metal sheet and composed of two circular portions each made curved in conformity with a circular outside surface of the rolling element and connected with one another, and an axial web disposed between the forward and aft circular portions to space the leading and trailing rollers away from one another. The retainer is constructed to guide the leading and trailing rolling elements with keeping their axes parallel with each other, while making certain of protecting securely the rolling elements against falling away from the retainer. Moreover, the retainer has guide portions extending sidewise beyond the axially opposite ends of the rolling element and bending at forward and aft ends thereof into U-shape. The retainer is allowed to run through the circulating circuit as the guide portions fit for sliding movement into grooves cut in widthwise opposite sides of the circulating circuit.
However, the linear motion guide unit constructed as stated just above also is not suited to shrink the linear guide unit in construction, because the retainer has the guide portions bent into U-shape that would need to make the grooves in the circulating circuit much larger. The retainer itself is extremely intricate in construction, which would need very sophisticated mold cavity in the injection molding process. In addition, the prior retainer recited just above, since made stiff or rigid in construction, is unsuited for smooth traveling to negotiate easily the turnaround passage curved sharply.
A further another sort of linear motion guide means is disclosed in the Japanese Patent No. 3343195, in which a roller chain is installed in a circulating circuit defined inside a slider that is allowed to move along and relatively to a guide rail. The roller chain gets looped to fit into the circulating circuit inside the slider. The roller chain is composed of many rollers, spacers each interposed between any two adjacent rollers, and flexible belts lying in sidewise opposition and integral with the spacers to connect them through the flexible belts to keep the rollers in rolling contact around their circular outside surfaces with their leading and trailing spacers, thereby making the rollers parallel with one another between their associated leading and trailing spacers.
With the roller chain of synthetic resin in which the spacers are integral with the lengthwise belts to form a molded product like a ladder and the rollers are each held between any leading and trailing spacers in succession inside the ladder, nevertheless, installation of the rollers inside the chain or ladder has to be performed by either molding the rollers themselves integrally with the chain or placing the rollers between any associated leading and trailing spacers after having molded the chain. In case where rollers are each placed between any leading and trailing spacers that have been molded in advance of installation of the rollers, any window to fit the roller therein has to be necessarily made at the same time molding the chain or ladder. To this end, an additional core must be placed in the mold cavity to provide the window after having withdrawn out of between any two adjacent spacers. This necessity of the additional core would often create a collateral problem of raising intricacy of assembled molds to withdraw successfully the cores without any interference with their associated spacers. Otherwise, it would be needed to extract the core out of the chain or ladder while making the associated leading and trailing spacers distorted by force. This forced extraction of the cores could likely cause either any permanent distortion or any damage in the chain or ladder. Forced extraction of the cores, moreover, would raise the issue negatively affecting the service life of the chain or ladder. The roller chain or chain retainer constructed as recited above, since moving in and out with high velocity while following the high-speed reciprocating motion of the slider, is always experience intense stress repetition of bending-stretching-compression and therefore more likely to shear off. Furthermore, the chain retainer, although made of synthetic resin rich in flexibility, is ready to swell with water, oil, and so on, thereby more likely to shear off.
The linear motion guide unit whose retainer fits into the circulating circuit in the slider is needed to meet a variety of requisites, the more important being to make the linear motion guide unit itself higher in mechanical stiffness or rigidity, to render the slider more withstanding against high-speed sliding operation relatively to the guide rail and high acceleration/deceleration relatively to the guide rail, to make the retainer possible to reserve lubricant therein, and to guide the rollers in good rolling order without leaning in rolling posture.
Aspects to be considered to cope with the requisites as stated earlier include the following:
(1) More stiffness in the linear motion guide unit can be accomplished with the guide rail that is designed to receive more rollers as many as permitted to carry the load, thereby providing the load-carrying race as long as possible.
(2) More withstanding property against high-speed and high acceleration/deceleration operations may be realized by the retainer that is refined in construction not to suffer any forced stress.
(3) The cylindrical rollers have higher tendency to displace much lubricant from the load-carrying race in the circulating circuit compared with balls, it is more needed to sustain more lubricant in the recirculating circuit for the rollers than for the balls, and moreover reserve much lubricant inside the retainer by itself.
(4) The rollers have to be not only born against their circular rolling surfaces, but also guided in sliding manner on their axially opposite ends.